This invention relates to a vacuum pump having a housing, a drive motor and an oil casing.
Vacuum pumps, particularly oil-lubricated, rotary vane vacuum pumps have low-noise characteristics provided that they are driven with a low rpm, that they have a relatively large mass and that the coolant air stream is weak. Further, to enhance low-noise characteristics, the "oil-knock" (caused by compression in the pumping chamber, particularly in the final pressure phase) is avoided by the admixture of leakage air.
The above-outlined measures, however, are inconsistent with the low-cost manufacture and good power data of the vacuum pump. Vacuum pumps operating at low rpm's and weak coolant air flow have a relatively low power density, that is, they have a large structural volume. An elimination of the oil-knock by the admixture of leakage air adversely affects the final pressure.